1. Field of the Invention
The present invention relates to a heater unit which is provided with a heater plate for heating, for example, a semiconductor substrate.
2. Description of the Related Art
In a semiconductor manufacturing process, for example, a heating apparatus for heating a semiconductor substrate accommodated in a process chamber is used. One example of such a heating apparatus is described in Jpn. Pat. Appln. KOKAI Publication No. 2003-133195.
A heating apparatus of this kind has a heater plate which houses a resistive heat generator. A heater plate is maintained at a desired temperature by performing current control on the resistive heat generator. A shaft portion is provided on a lower face side of the heater plate. A bottom face of the shaft portion is fixed to a heater mounting portion of a casing of the heating apparatus.
In the heating apparatus described in the above patent literature, a long size supporting member (corresponding to the shaft portion) is employed in order to reduce temperature fluctuation on a semiconductor placement face. The length of the supporting member is, for example, 250 mm.
In recent years, however, in order to achieve compactness of the semiconductor manufacturing apparatus, there is such a tendency that it is desired to reduce the length of the shaft portion. However, when the length of the shaft portion is reduced, heat of the heater plate easily transfers to a lower portion (a shaft bottom portion) of the shaft portion, so that the shaft bottom portion tends to become a high temperature.
A sealing member (a heat-resistant O-ring) for sealing the casing of the process chamber and the shaft portion with each other is provided on a bottom face of the shaft portion. An excessively high temperature of the shaft bottom portion causes a degradation of the sealing member (the heat-resistant O-ring) provided on the shaft bottom portion or loss of the sealing function thereof. In order to prevent such a drawback, it has been proposed to form a coolant flow path in the vicinity of a heater mounting portion of the casing. A portion of the shaft portion near to the bottom is forcibly cooled by causing coolant to flow in the coolant flow path.
In a short type shaft portion with a length of 50 mm or less, however, heat transfers between the heater plate and the shaft bottom portion more easily compared with a long type shaft portion with a length of more than 50 mm. Therefore, when the shaft bottom portion is cooled excessively, temperature reduction is caused at the central portion of the heater plate or the like, which results in deterioration of temperature evenness of the heater plate. That is, such a problem arises that a semiconductor substrate which is a material to be heated or the like cannot be heated accurately.